public class Point2D<T>
{
    public T x { get; set; }

    public T y { get; set; }

    public Point2D(T x, T y)
    {
        this.x = x;
        this.y = y;
    }
}

public class Z<T> : Point2D<T>
{
    public T z { get; set; }

    public Z(T x, T y, T z) : base(x, y)
    {
        this.z = z;
    }
}

public class Point3D<T>: Z<T>
{
    public Point3D(T x, T y, T z) : base(x, y, z)
    {
    }

    public string GetPoint()
    {
        return "x +" + x + " y +" + y + " z +" + z;
    }
}